Method for transferring layers produced in a vacuum

ABSTRACT

Method for constructing operational layers, such as photosensitive layers, outside the operational containers, such as camera tubes, in which they are to be used ultimately, testing the layers, then transferring them to the operational containers.

United States Patent [72] Inventors Heinrich Strublg Darmstadt; WernerTretner, Weiterstadt; Gunter Flasche, Dannstndt, all of Germany [21]Appl. No. 19,421

[22] Filed Mar. 13, 1970 [45] Patented Dec. 28, 1971 [73] AssigneeFernaeh Gmbll Darmstadt, Germany [32] Priority Mar. 27, 1969 [33]Germany [54] METHOD FOR TRANSFERRING LAYERS PRODUCED IN A VACUUM 10Claims, 2 Drawing Figs.

[52} U.S.Cl 316/4, 316/1, 316/10, 316/12, 316/19 [51] 1nt.Cl 1110139/18,l-lOlj 9/38 [50] Fleld 01 Search 316/17, 18, 19, 20,1, 3,4,l0,12;53/7,9

[56] References Cited UNITED STATES PATENTS 2,984,759 5/1961 Vine 316/17X 3,353,889 11/1967 Legoux Primary Examiner-John F. Campbell AssistantExaminer-Richard Bernard Lazarus Attorney-Littlepage, Quaintance, Wrayand Aisenberg ABSTRACT: Method for constructing operational layers, suchas photosensitive layers, outside the operational containers, such ascamera tubes, in which they are to be used ultimately, testing thelayers, then transferring them to the operational containers.

mama) 052281571 316130.590

In ven tor Dr Heinrich Sfrdbig Dr Werner Tretn er A ttornevs METHOD FORTRANSFERRING LAYERS PRODUCED IN A VACUUM BACKGROUND OF THE INVENTION 1.Field of the Invention The invention relates to a method fortransferring operational layers of various types, which have beenproduced in a vacuum and which are very sensitive to other gases, from afirst vacuum container into an operational vacuum container, in whichthe layer is to be used. The invention relates particularly to thetransfer of layers for forming photocathodes with photoelectric emissionfor these layers are extremely sensitive to other gases and a very highquality and homogeneity is desired. However, the invention is notrestricted to this application.

2. Description of the Prior Art In television camera tubes withphotocathodes, a layer is required which is very uniform over the entiresurface on which the image for transmitting is projected, and which isextremely sensitive and nearly completely free of spots, defects, etc.The known method for producing the photocathode directly in the cameratube result in a great amount of waste, since defects of thephotocathode can not be determined completely before the finalmanufacturing step. In this known method if the photocathode includesdefects or has too low a sensitivity and homogeneity, the whole cameratube must be scrapped.

SUMMARY OF THE INVENTION Therefore, it is highly desirable to have amethod for producing a layer, such as a photocathode layer, in aseparate area under optimum conditions; for example, in a separate bulbwhich includes all devices for producing the photocathode, but includesno other electrodes, so that this layer can be tested to determine thequality of the photocathode and to eliminate faulty units at this stageof the manufacturing process. During the further steps of this desiredmethod the tested photocathode must be removed from the bulb andtransferred to the tube, in which it will ultimately operate. This tubemay be a television camera tube or the like. However, the transfer ofsuch a layer from one unit to another is a step which is difficult tocarry out, since during the transfer the layer comes into contact withsurrounding environments which are different from the surroundings inwhich the photocathode has been produced and which have ensured itsstability. Moreover, it was discovered that the surroundings of thephotocathode in the new tube should conform to the surroundings in theoriginal chamber. If these conditions are not provided, the sensitivityof the photocathode after sealing in the new tube does not correspond tothe sensitivity in the original chamber where the photocathode wasproduced, and the sensitivity will decrease during storage.

Because of the above-mentioned difficulties, a corresponding method hasnot been discovered, or used, for conventional tubes which havesufficient room for one to place the devices for producing thephotosensitive layers in the tubes. In other devices not havingsufficient room for the device for producing the layer, as for instancein a so-called sandwich-imageconverter tubes" where the photocathode andthe screen are at a small distance from each other, attempts have beenmade to achieve the transfer by means of a vacuum bell jar surroundingboth the open image-converter tube without photocathode and the devicefor producing photocathodes. First the photocathode was produced in thebell jar and it was then transferred into the opening of the tube.However, this method does not permit testing of the photocathode beforetransferring it and does not permit elimination of faulty photocathodesbefore being transferred to the converter tube.

The method for producing a photosensitive (light-reactive) layer in animage-converter tube according to this invention avoids these and otherdisadvantages by producing the photosensitive layer in a closedcontainer which is not the ultimate container of the image-convertertube, testing the quality of the layer, e.g. by flying-spot scanning,preparing the image-converter tube and its electrodes, except thephotosensitive layer and the faceplate for supporting the layer, andinstalling these elements in a dismountable vacuum container, in whichthe container of the photocathode is also installed, evacuating thevacuum container, baking out the image-converter tube if necessary andtreating its inside wall to produce favorable surroundings into whichthe photosensitive layer may be inserted, separating the carrier of thephotosensitive layer from said container and bringing it quickly infront of the opening of the image-converter tube, connecting the carrierof the photocathode and the image-converter tube in a vacuum tightmanner, and finally ventilating the vacuum container and removing thefinished tube.

This instant method provides many technological and economicaladvantages. In the above-mentioned prior art method the transitionbetween the point of time, at which the photocathode is finished and thepoint of time at which it is installed in the other container isundetermined, since each photocathode acts differently during itsforming. On the other hand, the novel method hereof permits a short,exactly determinable time interval during which the photocathode is keptin the vacuum container which depends only on the mechanical conditionsof transfer. For instance, it is possible to separate the photocathodefrom the container and transfer it on to the other tube within 1 second.This very short period of time causes no damages to the photocathode inthe very high vacuum since the tube which will ultimately contain thephotocathode has been treated before to create conditions which ensurethe stability of the cathode. The previous testing to determine defectsand sensitivity of the photocathode guarantees an extremely low scraprate, which is particularly economical for the production of tubeshaving a very complex electrode arrangement. Finally, a tube is removedfrom the vacuum container which includes a high-quality photocathode.The method of this invention importantly permits production of tubeshaving a compact arrangements, which prevent installation of evaporationdevices for producing the photocathode. The produced tubes have a highersensitivity and a higher quality than the tubes produced according tothe known methods.

It has been discovered that in the production of photocathodes of type S20, it is advantageous to treat the faces of the inner parts of the tubeultimately containing the cathode with the vapor of one or more alkalimetals preferably potassium, sodium or cesium. For that purpose it issuitable to close the interior of the tube by a removable cover, bakeout the tube, evaporate potassium and sodium and/or cesium with anevaporator for the metal, cool down the tube and evaporate again anamount of alkali metal vapor, which condenses on the wall of the tubethereby forming metallic droplets which act as a reserve of alkalimetal. The source of alkali metal vapor may be located somewhere in thecontainer at a place where it does not affect the electroopticalfunction, e.g. close to the beam system. Then the photocathode isseparated from the first container and the photosensitive layer istransferred to the electron tube, simultaneously removing the cover fromthe tube, and the tube is closed by means of a suitable sealing method.

The separating of the photocathode carrier from the first container(auxiliary container) and the sealing of the photocathode carrier andthe electron tube may be facilitated by providing defined faces for thesealing of the container, for instance by grinding a wedge-shaped grooveinto the separating area with the wedge surface perpendicular to thecathode carrier and optically polished. The depth of the wedge-shapedgroove may be chosen so that the remaining wall-thickness is less than amillimeter, e.g. half a millimeter. Then a heated filament is insertedinto the wedge-shaped groove and heated, whereby the photocathodecarrier is separated (blown off) and a well-defined surface for theconnection of the photocathode carrier and the electron tube isproduced.

To connect the photocathode carrier and the electron tube, the so-called"cold-seal method" has been used with very satisfactory results. In thisknown method, a ring of indium, which has been freed of any residualoxide by burning off or by chemical treatment, is provided at the bondof both parts. Then the photocathode carrier is placed onto thecontainer carrying the ring of indium and pressed on, so that the indiumflows into the split between the two parts and is partially squeezedout, whereby the smooth edges of the photocathode carrier and theelectron tube are connected strongly, so that a good vacuumtight seal isachieved.

The vacuum in the finished electron tube is, of course, dependent on thevacuum in the surroundings, ie in the vacuum container, which enclosesthe electron tube as well as the first or auxiliary container. Usingmodern vacuum pumps, a vacuum of 10* can easily be achieved in adismountable vacuum chamber, which vacuum is sufficient for thestability of a photocathode within the transfer period. An elasticallyor plastically deformable metal body for transferring compressive forcesonto the tube from the outside may be used to accomplish the necessarymechanical pressure, thereby guaranteeing a vacuumtight connection ofthe electron tube and the photocathode carrier.

BRIEF DESCRIPTION OF THE DRAWINGS The method according to the inventionwill be described with the aid of the accompanying drawings and inwhich:

FIG. I is a schematic diagram of an apparatus to carry out the method.

FIG. 2 is a partial view of the first or auxiliary container 12 shown inFIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT FIG. 1 shows a dismantleablevacuum system comprising a baseplate l, a cylindrical glass body 2, acover plate 3, and a pump 4. The cover plate 3 can be removed afterventilation of the vacuum system. The following elements are installedin the vacuum apparatus: a swiveling device 5 having two arms 50 and 5b,a baking-out oven 6 for reception of the electron tube to be produced, asupporting device 7 for supporting the electron tube to be produced, apressing device 8, 9 and 10 comprising a plunger 8 mounted on a flexiblemetallic bellows 9 and adjustable in the vertical direction by means ofa threaded spindle and a handwheel 10. In the process of producing theelectron tube 11 the auxiliary container 12 is inserted into thisapparatus. The container 12 comprises a highly sensitive and pretestedphotocathode on the photocathode carrier 13, which is mounted on the arm5a by means of a gripping device. Thus, the carrier can be separatedfrom the auxiliary container and put down at another place by theswiveling device 5 after the groove 12a is cracked. The electron tube 11is held in the supporting device 7, located in the vacuum containeropposite the position of the photocathode. The supporting device 7permits adjustment and support of the electron tube 11. The tube isclosed by a cover 14 mounted on the arm 5b of the swiveling device 5. Aring of indium located on the upper edge of the open tube 11 (later usedfor melting or sealing) is shielded against radiant heat from the oven 6which encloses the tube and the supporting device. The oven 6 serves tobake out the tube whereby the rest of the water on the glass wall iseliminated. The electron tube 11 might be, for example, an imageorthicon including electrodes in an arrangement conventional for thosetubes. However, such a tube does not include evaporating devices forproducing the photocathode. In order to give the clear illustration ofthe invention, the figure does not show the electrical devices and theirwiring and the auxiliary mechanical devices, e.g. for stripping thephotocathode carrier 13 off the gripping clip. Moreover, the electricalequipment for producing alkali metal vapor within the tube 11 is notshown. Alkali metal evaporators are known in the art and need not bedescribed.

EXECUTION OF THE METHOD A finished electron tube is produced by means ofthe abovedescribed apparatus as follows. First the auxiliary container12 and the tube 11 are inserted, when the cover plate 3 is opened andthe arms 5a, 5b are set perpendicular to the plane of the drawing. Theauxiliary container and the tube are adjusted so that the plane of thegroove 12a of the auxiliary container 12 nearly coincides with the planeof the upper edge of the tube 11. Then the arms 5a and 5b are brought inthe position shown in FIG. I, and the upper portion of the auxiliarycontainer 12 comprising he photocathode carrier 13 is held by a grippingdevice. The auxiliary container 12 is selected to have certain qualitycharacteristics and to include a highly sensitive photocathode, free ofdefects. Now the opening of the glass cylinder 2 is closed by the coverplate 3, and the pump 4 starts generating a high vacuum in the vacuumcontainer and in the interior of the tube 11. It may be advantageous toplace the cover 14 only loosely on the tube 11 or to provide openings inthe cover to avoid substantial pressure differences between the interiorof the tube 11 and the interior of the vacuum container. Then the over 6is turned on and the interior of the tube is heated to the range fromabout 200 C. to 300 C. After that, alkali metal vapor is produced withinthe tube 11 by means of an evaporator (not illustrated), which may befed with electric current through supply leads at the socket or base ofthe tube. This working condition may be maintained for about 1 to 1%hours, after which the tube is cooled down, and after cooling down tothe range from about C. to C., alkali metal vapor is produced again.Then electric current is fed through leads (not illustrated) to theheated filament located at 12a in the wedge-shaped groove in the tube12, whereby the photocathode carrier is separated (blown off). Theswiveling device 5 is then actuated as fast as possible to bring thephotocathode carrier 13 in front of the opening of the electron tube 11by I80 rotation. The photocathode carrier is put down by a releasingmechanism, the arms of the swiveling device 5 is set in the positionperpendicular to the plane of the drawing, and then the pressing device8, 9 and I0 is actuated, which permits the exertion of pressure on thephotocathode carrier by means of the hand wheel 10. This pressure causesdeforming of the indium ring located in plane 15. The indium fills thespace between the edges of the photocathode carrier and the electrontube II so that vacuumtight sealing is achieved. Now the vacuum systemis ventilated, the cover plate 3 removed and the finished tube takenout. To achieve a good baking out of the upper part of the electrontest, it may be desirable not to place the ring ofindium on the upperedge of the open tube, but to fasten it on the photocathode carrier inan intermediate position of the swiveling device, since the indium meltsat 160C.

FIG. 2 shows a part of the auxiliary container 12 with the wedge-shapedgroove. In this figure, numeral 16 indicates a part of the container 12with the photocathode carrier I3 comprising the formed photocathodelayer 13a. A groove I7 is ground into the container wall by a diamondgrinding-wheel, which is shaped wedgelike. A wedge surface is arrangedexactly parallel to the photocathode carrier 13a. This surface will beprovided with an optical polish. To separate the photocathode carrier13, a thin tungsten filament is inserted into the wedge-shaped grooveand heated by a current pulse at the suitable time. Then the cathodecarrier 13 cracks off in an exactly defined plane, whereby the grooveensures that the force of separation coincides with the ground wedgesurface. Small variations are possible, but do not affect the tightnessof the sealing with the tube II, because of the resilience of the ringof indium. For exact adjustment of the photocathode carrier on electrontube 11 in relation to its axis, a gauge stop 18 may be provided againstwhich the hand wheel 10 abuts after a certain lifting of the pressingdevice 8, 9 and 10. The precision of this adjustment is at least equalto those of the conventional methods of melting the photocathode carrieran the container as used in the glass technology.

The invention includes some modifications not yet described. Forexample, the shape of the groove in the auxiliary container may besemicircular or rectangular, since the scaling is mainly accomplished inthe separation surface. Moreover, additional alkali metal vapor may beproduced in the already closed tube, for instance to correct thephotocathode.

According to another modification of the invention, the electron tubemay be produced without the transferred photocathode at first and beprovided with an auxiliary photocathode instead of the finalphotocathode. This auxiliary photocathode need not have high quality; itis only used to test the function of the remaining parts of the tube.

Therefore, the vacuum container comprises the camera tube having anauxiliary photocathode with a tested system and a container with atested photocathode of high quality.

To finish the camera tube both photocathodes are separated from theircontainers in the high vacuum of the vacuum container according to thedescribed method. Then the tested cathode is transferred to the testedelectron tube and placed into the opening produced by the separation ofthe auxiliary photocathode. The connection of the photocathode and theelectron tube corresponds to the above-described method, and thecold-seal method may be used.

I claim:

1. A method for producing an operational layer contained within anoperational container comprising the steps of A. producing theoperational layer on a carrier (13) in a closed container (12) outsidethe operational container,

B. testing the quality of the layer within the closed container,

C. providing the operational container l l including internal elementsother than the operational layer and support means for said layer, andenclosing the operational container and the closed container in adismantleable vacuum container (1,2,3).

D. evacuating the dismantleable vacuum container, heating theoperational container (11) and treating he inner surface of theoperational container to create favorable conditions in the operationalcontainer into which the operational layer may be inserted,

E. separating said carrier (13) from said closed container F. placingsaid carrier quickly into said operational container,

G. sealing the carrier and the operational container,

6. sealing the carrier and the operational container in a vacuum tightmanner, and

H. finally ventilating the dismantleable container and removing theoperational container.

2. A method according to claim 1 in which said operational layer is aphotosensitive layer and said operational container is a televisioncamera tube.

3. A method according to claim I wherein the step of treating the innersurface comprises producing metallic vapors within the operationalcontainer to treat said inner surface.

4. A method according to claim 3 wherein said metallic vapors are alkalimetal vapors.

5. A method according to claim 4 wherein the operational container iscooled down in the presence of said alkali metal vapors and is thenagain treated with alkali metal vapors.

6. A method according to claim 5 wherein the separation of said carrierfrom said closed container is enhanced by providing said closedcontainer with a wedge-shaped groove produced by grinding, whereby awedge surface is arranged perpendicular to said carrier and is opticallypolished.

7. A method according to claim 6 wherein a heated filament is insertedinto said groove and is momentarily heated so that said carrier iscracked off from the closed container.

8. A method according to claim 6 wherein a cover (14) is removed from anopening of the closed container during the quick transfer of saidcarrier (13) to an opening in the front of saidoperationalcontainer(ll).

9. method according to claim 1 wherein said sealing between the carrierand the operational container is achieved by inserting a ring of indiumin the connection region and by pressing the carrier onto the ring ofindium by mechanical force, whereby the space between the operationalcontainer (11) and the carrier (13) becomes sealed in a vacuumtightmanner.

10. A method according to claim 9, wherein a gauge is provided forlimiting the lift of a plunger which presses the carrier (13) onto theoperational container (11) whereby the exact position of the carrier inrelation to the axis of the operational carrier is determined when thegauge is touched.

UNlTED STATES PATENT OFFICE CEER'HFICATE 0F CORRECTION Patent No. 3 630590 Dated 2' 1 Q I fl Heinrich Strubig, Wernet Tretner, Gunter FlascheIt is certified that error appears in the above-identified patent andthat said Letters Patent arehereby corrected as shown below:

IN THE CLAIMS:

Claim 1, D., line 2, change "he" to -the-.

Claim 1, column 6, delete line 3 Signed and sealed this 27th day of June1 972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

2. A method according to claim 1 in which said operational layer is aphotosensitive layer and said operational container is a televisioncamera tube.
 3. A method according to claim 1 wherein the step oftreating the inner surface comprises producing metallic vapors withinthe operational container to treat said inner surface.
 4. A methodaccording to claim 3 wherein said metallic vapors are alkali metalvapors.
 5. A method according to claim 4 wherein the operationalcontainer is cooled down in the presence of said alkali metal vapors andis then again treated with alkali metal vapors.
 6. A method according toclaim 5 wherein the separation of said carrier from said closedcontainer is enhanced by providing said closed container with awedge-shaped groove produced by grinding, whereby a wedge surface isarranged perpendicular to said carrier and is optically polished.
 7. Amethod according to claim 6 wherein a heated filament is inserted intosaid groove and is momentarily heated so that said carrier is crackedoff from the closed container.
 8. A method according to claim 6 whereina cover (14) is removed from an opening of the closed container duringthe quick transfer of said carrier (13) to an opening in the front ofsaid operational container (11).
 9. A method according to claim 1wherein said sealing between the carrier and the operational containeris achieved by inserting a ring of indium in the connection region andby pressing the carrier onto the ring of indium by mechanical force,whereby the space between the operational container (11) and the carrier(13) becomes sealed in a vacuumtight manner.
 10. A method according toclaim 9, wherein a gauge is provided for limiting the lift of a plungerwhich presses the carrier (13) onto the operational container (11)whereby the exact position of the carrier in relation to the axis of theoperational carrier is determined when the gauge is touched.